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Today's Ve T erinary Prac T ice | s eptember/ o ctober 2016 | tvpjournal.com Ju V enile o r T ho P edic d isease in d ogs & c a T s Peer r eviewed 24 Juvenile orthopedic diseases affect the musculoskeletal system of immature animals, and most of these diseases can be traced to pathologic events (eg, diseases, toxins, inappropriate nutrition, trauma) occurring in this period. This 2-part series addresses the most common pathologic conditions affecting juvenile dogs and cats, including: • Congenital and neonatal orthopedic diseases: Defined, for these articles, as diseases that occur in the prenatal period or within the first 3 to 4 weeks of life • Pediatric bone, cartilage, and joint diseases: Diseases that occur in the skeletally immature dog. Part 1 of this series presented an overview of musculoskeletal development and pediatric bone diseases (diseases that occur after 1 month of age and before skeletal maturity), which generally have a good prognosis. This article discusses congenital and neonatal orthopedic diseases as well as pediatric cartilage and joint diseases. CONGENITAL & NEONATAL ORTHOPEDIC DISEASES Neonatal diseases are apparent at birth or within the first 3 to 4 weeks of life. While these diseases are often congenital and inherited, a direct cause for each disease has not yet been determined, and other causes, such as in utero factors, may play a role. Such diseases can be categorized according to the tissue affected. For example, dysostoses refer to diseases of individual bones or a defect in mesenchymal bone formation, whereas osteochondrodysplasia refers to defects of endochondral or intramembranous ossification. 1 Part 1 of this series—Musculoskeletal Development & Pediatric Bone Diseases (May/June 2016)— presents a basic overview of the steps of ossification. A thorough history is crucial and useful in obtaining a diagnosis; it should include information regarding: • Age at which the disease became apparent • Whether other littermates or relatives have similar presentations • Breeding environment and general care of the dam and puppies (eg, raised in "puppy mill") • Exposure to medications or radiation • Maternal health. Dysostoses Overview A dysostosis is a defect in the development of a bone or part of a bone. 1-3 In contrast, a synostosis is a defect in the development of 2 or more adjacent bones, leading to fusion. Dysostoses result from 1 or more failures in proper development of mesenchymal bone, transformation of the mesenchymal bone model into cartilage, or conversion of cartilage into bone. Such defects can occur in the axial or appendicular skeleton. 2,3 Axial dysostoses include hemivertebra, block vertebra, butterfly vertebra, transitional vertebra, spina bifida, facet aplasia, and dens malformation 4 ; the most commonly encountered axial dysostoses are summarized in Table 1. Consequence of such malformations can lead to varying degrees of spinal cord or nerve root compression and, thus, varying degrees of subsequent neurologic dysfunction. 4,5 Furthermore, any of these conditions can be seen in the absence of clinical signs, and their presence alone does not necessarily warrant intervention. For example, hemivertebra often results in characteristic spinal angulation at the site of the defect, as seen by kyphosis, lordosis, or scoliosis. 4 Any breed can be affected by such conditions (Table 1) and, while few direct cause-and-effect relationships have been determined, many of these conditions are likely inherited. 4 Juvenile Orth O pedic d isease in dO gs & c ats Part 2: Congenital & Neonatal Orthopedic Diseases Shannon Kerrigan, VMD, and Duane Robinson, DVM, PhD, Diplomate ACVS (Small Animal) University of California–Davis